Compression Behaviour of Concrete Cylinder with Carbon Fibre Reinforced Polymer (CFRP) Confinement

Carbon fibre reinforced polymer (CFRP) confinement has always been one of the strengthening methods available for a vulnerable concrete column. This paper presents the compressive behaviour of nine circular concrete cylinders with CFRP confinement. Three different specimen conditions considered; full CFRP confinement, partial CFRP confinement and unconfined (control specimen). Nine concrete cylinders with 100 mm x 200 mm were tested under compression load. It is discovered that full and partial CFRP confinement had improved concrete cylinder ultimate load capacity by 300% and 150% respectively when compared to the unconfined concrete cylinder. With 150% strength enhancement achieved by partial CFRP confined specimen, it is proven that partial CFRP confinement does provide sufficient confinement in enhancing concrete column strength as full CFRP confinement. This finding has led to remarkable discoveries which with lesser CFRP used the functionality of CFRP as strengthening material can still be utilized. Therefore, could contribute significant input to the construction industry in using lesser CFRP for more sustainable material approach.

Effect of Carbon Fibre Reinforced Polymer Strengthening on Axial Capacity and Ductility of Non-slender Square Concrete Columns

This research investigated the effect of Carbon Fibre Reinforced Polymer (CFRP) strengthening on the axial capacity and ductility of non-slender square concrete columns. There was a problem of buildings collapsing in Kenya. Retrofitting of the buildings vulnerable to collapse was of great importance to ensure the safety of the occupants and to address the housing deficit in the country. An experimental research programme was conducted on 90 non-slender square concrete columns to find out the gain in axial capacity and ductility of the columns strengthened by CFRP. The specimens (150mm x 150mm x 350mm) were made of plain and reinforced concrete. Three different concrete grades: C8/10, C12/15 and C16/20 were used. The specimen had varying configurations of CFRP wrap: partial and full confinement in one and two layers. Four parameters were investigated in this study: concrete grade, steel reinforcement, degree of confinement and the number of layers of CFRP wrap. The specimens were subjected to uniaxial compression up to failure, and the stress-strain curves were plotted. This study found that weaker concrete grades experienced the highest effect due to CFRP strengthening. Presence of reinforcement had a significant effect on the axial capacity and ductility of columns without CFRP strengthening. On the contrary, the presence of steel reinforcement reduced the effectiveness of CFRP strengthening. Partial CFRP confinement offered better material efficiency as compared to full CFRP confinement, and the number of layers had a direct relationship with the increase in strength and ductility.

Experimental Investigation of RC Columns Confined with Ni-Ti Shape Memory Alloys Wires versus CFRP Sheets

The critical need to enhance existing strengthening methods with more efficient and effective ones has led to the evolvement of smarter and innovative class of materials termed Shape Memory Alloys (SMA). The SMA’s possess unique characteristic properties that lie in their ability to undergo large deformations and return to their undeformed shape through stress removal or heating process. Limited research studies conducted using SMA’s have shown high potential for their use in building industry. Results presented in this research study are from an experimental study that investigated the compressive behaviour of uniaxial concentrically loaded Nickel – Titanium (Ni-Ti) SMA-spirally confined RC columns and compared with RC columns confined with conventional CFRP sheets. The compression tests revealed that actively confining the concrete column with Ni-Ti SMA spiral wires increased the performance of the concrete dramatically. Additionally, the active Ni-Ti SMA-confinement system exhibited superior performance compared to the conventional passive CFRP-confinement system.

Assessment of Standards and Codes Dedicated to CFRP Confinement of RC Columns

Reinforced concrete (RC) columns are often placed under confinement to increase their strength and ductility. Carbon fiber reinforced polymer (CFRP) materials have recently been recognized as favorable confinement systems. At present, a number of national standards and codes dedicated to the design of concrete components strengthened with CFRP in general and CFRP confinement in particular are available. These sets of rules provide design equations for confined reinforced concrete columns with circular and rectangular cross sections. Most of the standards and codes exhibit significant differences, including the used predictive models, limitations, observed effects and covered loading conditions. In this paper, five international standards and design guidelines are introduced and discussed. The purpose is to present a constructive and critical assessment of the state-of-the-art design methodologies available for CFRP confined RC columns and to discuss effects not previously considered properly. Therefore, some recent research efforts and findings from the Leipzig University of Applied Sciences are also introduced. The obtained data is used for a comparative study of the guideline predictive equations. Furthermore, it is shown that some new findings concerning the rupture strength and the maximum strength plus accompanying axial strain of a CFRP confined column are suitable to improve the current guidelines.